Subjective well-being (SWB) researchers examine the causes and correlates of life satisfaction, positive affect, and negative affect. Research shows that these well-being variables are stable over time and often change only slightly following major life events and changes in life circumstances. In addition, SWB constructs often correlate more strongly with stable personality traits such as extraversion and neuroticism than they do with other intuitively predictors such as health, income level, or marital status. Thus, to understand the causes of well-being and to develop theories that will ultimately be able to promote higher levels of well-being, researchers must look with persons to the personality processes that underlie these individual differences. In the proposed research, the PI will conduct a 9-month long longitudinal study using a variety of research methods (including intensive sampling of emotions and behaviors over time, experimental mood induction procedures, and informant reports of emotion and personality) to investigate one of the strongest and most consistent findings in the study of personality and emotion the moderate to strong correlation between extraversion and positive effect. Three theories have been proposed to account for this relation. According to these theories, extraverts are happier than introverts because: (a) Extraverts spend more time in social situations than do introverts and social situations increase positive effect; (b) Extraverts create more positive life circumstances than do introverts; or (c) Extraverts react more strongly to pleasant stimuli than do introverts. The primary aim of the proposed research is to test these hypotheses simultaneously to determine whether they can fully account for the differences in extraverts' and introverts' positive affect. A second aim is to determine the causal direction of the extraversion/positive affect relation. A final aim is to investigate the psychometric properties (including long-term reliability and predictive validity) of experience sampling measures of personality and emotion. The findings will not only increase understanding of the extraversion/positive affect relation; they will also have important implications for more general theories about the nature of extraversion, the causes of subjective well-being, and the function of positive affect. The results will also have implications for researchers' use of experience sampling measure of personality and emotion.